Quote:

Code:

{10 15 25}   {20 10 15}   {30 + 25 + 40}
{ 5 20 10} + (15  5 40} = {20 + 25 + 50}
{30  0  5}   {10 20 25}   {40 + 20 + 30}

And is it the same thing as if you multiply or divide?



The above is wrong. Matrix addition is done element-wise.
Code:

(a11 a12)   (b11 b12)   (a11+b11 a12+b12)
(a21 a22) + (b21 b22) = (a21+b21 a22+b22)
Same thing for subtraction- just replace the plus with a minus. Matrix multiplication is done by multiplying rows of matrix A with each column of matrix B. The matrix-vector multiplication I wrote about above is only a special case where the second matrix is a vector, i.e. a single-column-matrix.
Matrix division does not exist. But you can (sometimes) do a matrix multiplication with an inverse matrix which is similar to a division.

There is an excellent website covering all fields of mathematics:
http://mathworld.wolfram.com/

I also highly recommend the math program "Derive" which is a bit expensive for hobby users, but there is a 30-day-trial allowing you to play around with matrix and vector equations.